1. Field of the Invention
The present invention relates to a semiconductor laser device and an optical pickup apparatus using the laser device, and more particularly, to the structure of a mechanism for controlling the optical axis of a light beam exiting from a semiconductor laser device.
2. Description of the related Art
There has been sought ever-smaller and ever-denser information equipment using an optical information recording medium, such as a CD-R drive, a CD-RW drive, and a DVD drive. In connection with an optical pickup apparatus which writes, reproduces, and erases information by means of gathering a light beam emitted from a semiconductor laser device onto an optical information recording medium, demand exists for miniaturization as well as for an improvement in the accuracy of gathering of light onto the optical information recording medium.
FIG. 69 shows a related-art semiconductor laser device described in, e.g., Japanese Patent Application Laid-Open No. 77604/1994. FIG. 70 is across-sectional view taken along line 70—70 shown in FIG. 69.
As shown in FIGS. 69 and 70, reference numeral 200 designates a semiconductor laser device; 202 designates a semiconductor laser element; 204 designates a silicon base; 206 designates a metal frame; 206a designates notched grooves for positioning purpose; 208 designates a resin-molded protective wall; 208a designates an upper portion of the protective wall; 208b designates a lower portion of the protective wall; 210 designates a die-bonding material; 212 designates an electrode lead; and 214 designates a wire lead.
FIG. 71 is a partial plan view of a related-art optical pickup apparatus equipped with a semiconductor laser device 200.
As shown in FIG. 71, reference numeral 220 designates an optical pickup apparatus; 222 designates an assembly having mounted thereon an optical component (not shown) constituting an optical system for gathering a light beam exiting from the semiconductor laser device 200 and directing the same onto an optical information recording medium; and 224 designates a support. The support 224 attaches the semiconductor laser device 200 to the assembly 222. Further, by means of the support 224 being fitted to the notched groove 206a formed in the metal frame 206 of the semiconductor laser device 200, the support 224 positions the semiconductor laser device 200 to the assembly 222.
Reference numeral 226 designates an adjusting screw for attaching the support 224 to the assembly 222. By means of regulating the extents to which the right-side and left-side adjusting screws 226 are fastened, the angle of an optical axis of the light beam exiting from the semiconductor laser device 200 is adjusted.
In relation to the optical pickup apparatus 220 having such a structure, when the semiconductor laser element 202 of the semiconductor laser device 200 is die-bonded, the semiconductor laser element 202 is die-bonded to the silicon base 204, and the silicon base 204 is die-bonded to the metal frame 206. Hence, a positional error stemming from bonding inevitably arises. As a result, a mismatch arises in an optical axis of the optical system of the assembly 222 and the optical axis of the light beam exiting from the semiconductor laser device 200.
In the event of occurrence of a mismatch between the optical axes, power becomes deficient when information is written onto the optical information recording medium. As a result, a characteristic of the optical pickup apparatus is deteriorated, and accurate writing operation is not performed, thus inducing an operation failure. In order to prevent occurrence of such an optical problem in the optical pickup apparatus 220, there is a necessity for realizing a match between the optical axes of the optical pickup apparatus 220 through adjustment.
In the related-art optical pickup apparatus 220, the support 224 is fitted to the notched groove 206a formed in the metal frame 206 of the semiconductor laser device 200, thereby positioning the semiconductor laser device 200 relative to the assembly 222. The support 224 is fixed to the assembly 222 with the adjusting screws 226. Since the position of the support 224 is defined with the adjusting screws 226, a horizontal deviation in the optical axis of the optical beam cannot be absorbed, which in turn induces occurrence of horizontal misalignment between the optical axis of the optical beam of the semiconductor laser element 202 and the optical axis of the optical system of the assembly 222.
Since a horizontal angular misalignment of the optical beam exiting from the semiconductor laser device 200 deteriorates jitter, required accuracy of the optical axis of the outgoing light is, for example, ±0.3 degrees. Jitter is impervious to vertical angular misalignment, and hence the vertical angular misalignment presents no substantial problem.
In order to satisfy such required accuracy, the related-art optical pickup apparatus 220 performs angular adjustment of the optical axis of the outgoing light by means of adjusting right-side and left-side adjusting screws 226 for fastening the supports 224 to the assembly 222. However, rotational adjustment performed by the adjusting screws 226 also results in parallel movement of a light-emitting point, thereby inducing a horizontal deviation. The adjustment mechanism using the adjusting screws 226 has a structure less apt to absorb a horizontal deviation, thus posing difficulty in performing sheer angular alignment.
FIG. 72 is a schematic view for describing movement of the light-emitting point through related-art angular adjustment of the optical axis.
As shown in FIG. 72, reference symbol C0 designates the direction of optical axis of the optical system of the assembly 222. At the outset, the optical axis of the light beam exiting from the light-emitting point of the semiconductor laser element 202 situated at point 0 is oriented in direction C. Provided that the optical axis is re-oriented toward direction C1 through rotational adjustment by means of the adjusting screws 226, the light-emitting point of the semiconductor laser element 202 often moves to point O1. Thus, difficult is encountered in minute angular adjustment without moving the position of the light-emitting point.
A related-art example mechanism described in, e.g. Japanese Patent Application Laid-Open No. 203403/1994, is not a mechanism for adjusting an angle of optical axis of a light beam, such as that performed by the previously-described optical pickup apparatus 220, to correct angular misalignment in the optical axis of outgoing light associated with a deviation in the semiconductor laser element 202 or an assembly failure, but a rotation angle adjustment mechanism for effecting tracking control.
FIG. 73 is a plan view of another related-art semiconductor laser device. FIG. 74 is a cross-sectional view of the semiconductor laser device taken along line 74—74 shown in FIG. 73.
As shown in FIGS. 73 and 74, those reference numerals which are identical with the reference numerals shown in FIGS. 69 and 70 designate identical or corresponding elements. Even in the following drawings, like reference numerals designate like or corresponding elements.
As shown in FIGS. 73 and 74, reference numeral 230 designates a semiconductor laser device; and 232 designates a mirror made of silicon which reflects the optical axis of the light exiting from the semiconductor laser element 202 to an orthogonal direction. Reference numeral 234 designates a hologram unit; 234a designates a grating pattern; and 234b designates a hologram pattern for the purpose of splitting a beam. The hologram unit 234 is omitted from FIG. 73.
FIG. 75 is a plan view showing a related-art mirror and semiconductor element. FIG. 76 is a cross-sectional view of the mirror and semiconductor laser element taken along line 76—76 shown in FIG. 75. “L” designates an optical axis of the light that has originated from the semiconductor laser element 202 and has been reflected at an angle of 90° by the mirror 232.
The rim of a protective wall upper portion 208a is formed into a circular-arch shape centered on the optical axis L of the light that has originated from the semiconductor laser element 202 and has been reflected by the mirror 232 in an orthogonal direction.
FIG. 77 is a partially-perspective plan view of the related-art optical pickup apparatus using the semiconductor laser device 230.
As shown in FIG. 77, the circular-arch rim of the protective wall upper portion 208a of the semiconductor laser device 230 is fitted to a circular-arch guide 236 formed in the assembly 222. The semiconductor laser device 230 is provided on the assembly 222 so as to be rotatable about the optical axis L of the light that has originated from the semiconductor laser element 202 and has been reflected by the mirror 232 to an orthogonal direction. After having been subjected to optical axis alignment, the semiconductor laser device 230 is secured on the assembly 222.
In order to effect tracking control in accordance with the three-beam method, the optical system semiconductor laser device 230 must rotate the light originated therefrom by way of the hologram unit 234 through a predetermined angle with respect to the direction of a track of an information recording medium. Therefore, the protective wall upper portion 208a of the optical system semiconductor laser device 230 is slid along the circular-arch guide 236 provided on the assembly 222 and rotated about the optical axis L, thus aligning the optical axis of the light.